We should use UserID object to identify users instead of username.

chrome/browser/ui/webui/flags_ui.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/ui/webui/flags_ui.h"
 
 #include <string>
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
@@ skipping 215 matching lines @@
   about_flags::ConvertFlagsToSwitches(flags_storage_.get(),
                                       &user_flags,
                                       about_flags::kAddSentinels);
   base::CommandLine::StringVector flags;
   // argv[0] is the program name |base::CommandLine::NO_PROGRAM|.
   flags.assign(user_flags.argv().begin() + 1, user_flags.argv().end());
   VLOG(1) << "Restarting to apply per-session flags...";
   chromeos::DBusThreadManager::Get()
       ->GetSessionManagerClient()
       ->SetFlagsForUser(
-          user_manager::UserManager::Get()->GetActiveUser()->email(), flags);
+          user_manager::UserManager::Get()->GetActiveUser()->GetUserID(), flags);
 #endif
   chrome::AttemptRestart();
 }
 
 void FlagsDOMHandler::HandleResetAllFlags(const base::ListValue* args) {
   DCHECK(flags_storage_);
   about_flags::ResetAllFlags(flags_storage_.get());
 }
 
 
@@ skipping 83 matching lines @@
   registry->RegisterListPref(prefs::kEnabledLabsExperiments);
 }
 
 #if defined(OS_CHROMEOS)
 // static
 void FlagsUI::RegisterProfilePrefs(user_prefs::PrefRegistrySyncable* registry) {
   registry->RegisterListPref(prefs::kEnabledLabsExperiments);
 }
 
 #endif